Beam convergence device for color picture tube

ABSTRACT

In a cathode-ray tube in which a plurality of electron beams are focused on a screen by a focusing lens from which at least certain of the beams emerge along paths divergent with respect to the tube axis, and each of the beams emerging along a divergent path is deflected to cause convergence of the beams at a common area of the screen; such deflection of each diverging beam is effected by a pair of plates at different electrical potentials disposed at opposite sides of the respective divergent path and an auxiliary electrode having open areas therein disposed along the outer side of the respective divergent path spaced inwardly from the plate which is at the side of the respective divergent path away from which the beam is deflected, this plate being at a relatively low potential and the auxiliary electrode and the other plate being at substantially the same relatively high potential to establish an electric field between the plates which, in the region thereof located between the other plate and the auxiliary electrode and being traversed by the respective beam, has a potential gradient that is maintained substantially constant irrespective of variations in the relatively high potential to avoid misconvergence due to such variations.

United States Patent [72] Inventors Aitio Qhgoshi Tokyo; Senri Miyaoka, Fujisawa-shi, both of Japan [21] Appl. No. 874,568 [22] Filed Nov. 6, 1969 [45] Patented Oct. 19, 1971 73] Assignee Sony Corporation Tokyo, Japan [32] Priority Dec. 26, 1968 [33] Japan [3 l 43/945207 [54] BEAM CONVERGENCE DEVICE FOR COLOR PICTURE TUBE 8 Claims, 9 Drawing Figs.

[52] US. Cl 313/70 C, 315/13 C, 315/D1G. 3 [51] Int. Cl .Q H0lj 29/50 [50] Field ofSearch 313/69 C, 70 C, DIG. 3, 80; 315/13 [56] References Cited UNITED STATES PATENTS 3,448,316 6/1969 Yoshida etal. 3l3/69C 3,462,638 8/1969 Tetsuo et al. 315/13 Primary Examiner-Roy Lake Assistant Examiner-V. Lafranchi Att0rneysLewis H. Eslinger, Alvin Sinderbrand and Curtis,

Morris & Safford ABSTRACT: In a cathode-ray tube in which a plurality of electron beams are focused on a screen by a focusing lens from which at least certain of the beams emerge along paths divergent with respect to the tube axis, and each of the beams emerging along a divergent path is deflected to cause convergence of the beams at a common area of the screen; such deflection of each diverging beam is effected by a pair of plates at different electrical potentials disposed at opposite sides of the respective divergent path and an auxiliary electrode having open areas therein disposed along the outer side of the respective divergent path spaced inwardly from the plate which is at the side of the respective divergent path away from which the beam is deflected, this plate being at a relatively low potential and the auxiliary electrode and the other plate being at substantially the same relatively high potential to establish an electric field between the plates which, in the region thereof located between the other plate and the auxiliary electrode and being traversed by the respective beam, has a potential gradient that is maintained substantially constant irrespective of variations in the relatively high potential to avoid misconvergence due to such variations.

Oia 400% 066001 M24041.

PAIENTEDncI 19 ISZI SHEET 2 [1F 3 m GI INVENTORS AK l O OHGOSHI SE NR! MIYAOKA i E a ATTORNEY m w v v w I BEAM CONVERGENCE DEVICE FOR COLOR PICTURE TUBE This invention generally relates to cathode-ray tubes and more particularly is directed to improvements in the electrostatic convergence device of such tubes of the plural-beam type, by which the electron beams are converged on the electron receiving screen of the tube.

In existing cathode-ray tubes of the plural-beam type utilizing an electrostatic beam convergence system, such as the single-gun, plural-beam cathode-ray tube described in U.S. Pat. No. 3,448,316, the plural beams are made to pass through the center of a common electrostatic main focusing lens by which they are focused on a beam-receiving screen. At least certain of the beams emerge from the focusing lens along paths that are divergent, with respect to the tube axis, and the beams are thereafter passed through an electrostatic convergence device as to converge the beams at a common area of the screen.

In cathode-ray tubes of the above-described type, the electrostatic beam convergence device comprises at least a pair of conductive plates spaced from each other, the plates being at different potentials. One of the plates has a high potential applied thereto, which is typically the anode potential of the tube, while the other plate has applied thereto a relatively lower potential, which is typically a potential of 200 to 300 volts lower than the higher anode potential of the one plate. The potential difference between the plates causes an electric field therebetween, so that an electron beam passing between theseplates is deflected a predetermined amount by the electric field and is consequently converged on the common area of the screen.

The amount of deflection experienced by the electron beam passing between the plates is dependent on the electric field created between the plates. In the existing electrostatic convergence devices, the electric field which effects the deflection of the beam, and hence its convergence with other beams, is solely dependent on the potential difference between the anode potential, which is the potential of one plate, and the potential several hundred volts lower than the anode potential, which is the potential of the other plate. The anode voltage may vary in accordance with a change in the operating conditions of the tube, for example, in accordance with changes in the brightness of the picture on the screen. However, the potential of the other plate, which is several hundred volts lower than the anode potential, has a relatively constant value regardless of variations in the anode potential, and the potential of the other plate will, therefore, remain relatively constant. As a result, the variations in the anode potential will cause variations in the potential difierence between the plates, thereby causing variations in the deflection of the beams due to changes in the electric field between the plates. This results in misconvergence of the beams which produces an undesirable affect on thepicture.

Prior art attempts at avoiding this misconvergence have required additional circuitry which have undesirably complicated the convergence circuit. For example, one such attempt involved undesirable additional circuitry for changing the lower potential in proportion to changes in the anode potential so as to maintain a constant potential difference between the plates.

Accordingly, it is an object of this invention to provide a new and improved plural-beam cathode-ray tube having a convergence system which overcomes the foregoing disadvantages of the prior art.

Another object of this invention is to provide a plural-heam cathode-ray tube with an electrostatic beam convergence system which avoids misconvergence of the beams by reason of variations in the anode potential of the tube.

In a cathode-ray tube according to an aspect of this invention, for example, in a color picture tube in which a plurality of electron beams are made to converge or cross each other substantially at the optical center of an electrostatic focusing lens by which the beams are all focused on the electronreceiving screen of the tube so that at least certain of the beams emerge from the focusing lens along paths that are divergent with respect to the tube axis, and those beams which emerge along the divergent paths are deflected by deflection means located between the focusing lens and the screen to cause convergence of the beams at a common area on the screen; the deflection means for each of the beams emerging along a divergent path is constituted by inner and outer spaced plates disposed along the respective divergent path at the inner and outer sides, respectively, thereof considered with respect to the tube axis, and an auxiliary electrode disposed along the outer side of the respective divergent path and being spaced inwardly from the outer plate, the auxiliary electrode and the inner plate being at substantially the same relatively high potential, for example, the anode potential, and the outer plate being at a relatively low potential, for example, at ground potential, to establish an electric field between the inner and outer plates which, in the region thereof located between the inner plate and the auxiliary electrode and being traversed by the respective beam, has a potential gradient that is maintained substantially constant irrespective of variations in the relatively high potential to avoid misconvergence of the beams due to such variations.

In a deflection means for a cathode-ray tube, as aforesaid, the auxiliary electrode has open areas to permit the electric field to penetrate therethrough, and such open areas may be defined by forming the auxiliary electrode as a parallel array of straight conductors spaced from each other and extending transversely or parallel with the longitudinal axis of the tube, as a plate having apertures, or as a plate having interconnected longitudinally and transversely extending conductive wires.

The above, and further objects, features and advantages of the invention, will appear from the following detailed description of illustrative embodiments of the invention which is to be read in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagrammatic axial sectional view of an existing single-gun, plural-beam cathode-ray tube which includes an electrostatic beam convergence device;

FIG. 2 is a diagrammatic view illustrating the character of the electrical field produced between two of the plates in the electrostatic beam convergence device of FIG. 1 for deflecting the beam passing between such plates;

FIG. 3 is a view similar to that of FIG. 1, but illustrating a cathode ray tube having an electrostatic beam convergence device according to an embodiment of this invention;

FIG. 4 is a view similar to that of FIG. 2, but illustrating the character of the electrical field produced between two of the plates in the beam convergence device of FIG. 3;

FIG. 5 is a graphical representation of the potential distributions and field intensities at two locations between the plates shown on FIG. 4; and

FIGS. 6A, 6B, 6C and 6D are diagrammatic perspective views of auxiliary electrode arrangements that may be employed in place of the arrangements of FIGS. 3 and 4 in accordance with this invention.

In the following detailed description of illustrative embodiments of the invention, reference is made to single-gun, pluralbeam color picture tubes, but it is to be understood that the electrostatic convergence devices according to the invention can be applied to any other cathode-ray tubes in which plural electron beams are required to be deflected for convergence at a common area of the screen.

Referring to the drawings in detail, and initially to FIG. 1 thereof, it will be seen that the existing type of single-gun, plural-beam cathode ray tube there shown includes electron beam generating sources constituted by three electrically separated cathodes KR, KG and KB to which red, green" and blue" video signals are respectively supplied. The three cathodes are arranged with their electron emitting surfaces in a straight line so as to be aligned with similarly arranged apertures gllR, gIG and 313 in a platelike first grid GI. A second cup-shaped grid G2 has an end plate disposed adjacent grid GI and formed with three apertures 32R, gZG and g2B which are respectively aligned with apertures gIR, glG and 31B.

Arranged in order following the grid G2 in the direction away from control grid G). are successive, open-ended, tubular grids or electrodes G3, G4 and G5. Electrode G3 includes relatively small diameter end portions 3 and d and a larger diameter intermediate portion 5, and is supported with its end portion 3 extending into cup-shaped grid G2 and spaced radially from sidewall 2 of the latter. Electrode G4 includes end portions 6 and 7 of a diameter larger than that of end portions 3 and t of electrode G3 and electrode G4 is mounted so that end portion 4 extends into, and is spaced radially inward from end portion 6. Electrode G5 includes an end portion 9 of a diameter smaller than that of end portion 7 and a relatively larger diameter portion 10, and electrode G5 is mounted so that its end portion 9 extends into, and is spaced radially inward from end portion 7 of electrode G4. The several electrodes G3, G41 and G5, grids 611, G2 and the cathodes KR, KG and KB are all assembled together in the above described relation by means of suitable supports (not shown) of insulating material.

In operating the electron gun of FIG. ll, appropriate voltages are applied to grids Gll and G2 and to electrodes G3, G4 and G5. For example, a voltage of to 400 v. is applied to the grid G l, a voltage ofO to 500 v. is applied to the grid G2, a voltage of B3 to 20 kv. is applied to the electrodes G3 and G5, and a voltage of 0 to 400 v. is applied to the electrode G4, with the voltage of the cathodes as the reference. Therefore, the voltage distributions with respect to the grids and electrodes G1 to G5, and their lengths and diameters may be substantially identical with those of a unipotential single-beam type of electron gun which includes a first single-grid member and a second grid provided with a single aperture. With the applied voltage distribution described above, an electron lens field is established between grid G2 and the end 3 of electrode G3 which corresponds to an auxiliary lens L, shown by broken lines, and an electron lens field corresponding to a main lens L shown by broken lines, is formed at the axial center of electrode G4 by the electrodes G3, G4 and G5.

In order to cause convergence of the beams BB and BR which emerge from electrode G along divergent paths, the electron gun of HG. E further has an electrostatic beam convergence device F that includes inner shielding plates P, and P, provided in spaced opposing relationship to each other and extending axially from the free end of electrode G5. Deflecting means F further includes outer plates P, and P,', which are shown to be planar and mounted in parallel, spaced opposing relation to the outer surfaces of inner plates P, and P respectively. Although plates P and P, are shown to diverge in the direction away from electrode G5, such plates may be parallel to the tube axis, with the outer plates P, and P, continuing to diverge, as shown, or also extending parallel to the tube axis. The plates P and P, and the plates P, and P, are disposed so that the beams BB, BG and BR pass between the plates P, and P,, between the plates P, and P and between the plates P, and P,, respectively. A voltage equal to that imparted to the electrode G51", such as the anode potential, is applied to the plates P, and P and a voltage lower than that applied to the plates P, and P, by 200 to 300 v. is applied to the plates P, and P,. Thus, deflecting voltage differences are applied between the plates P, and P, and between the plates P, and P, which respectively constitute the deflectors and are adapted to impart the deflecting action to the beams BB and BR, respectively, so as to deflect the beams BR and BB toward the center beam BG so that the three beams, BR, 80 and BB are converged to a common area on the screen.

Thus, the three beams BR, BG and BB emanating from the cathodes KR, KG and KG are made to pass through the apertures gllR, gllG and gm of grid Gil and are modulated with three different signals applied between the respective cathodes and grid G1. The beams, BR, BG and BB pass through the common auxiliary lens L which is formed mainly by the grid G2 and electrode G3 and cross each other substantially at the optical center of the main lens L which is constituted mainly by the electrodes G3, Gd and G5. Then, the beams BB, BG and BR pass between the plates P, and P,

between the plates P and P, and between the plates P, and P,, respectively, after having left the electrode G5. Since plates P, and P,' are at the same potential, beam BG is not deflected, but the beams BB and BR which emerge from lens L along divergent paths are deflected, so that the three beams are made to converge or cross each other at an aperture of a beam selecting aperture grill or shadow mask Gp and then diverge therefrom to impinge on a color screen S, comprised of sets of red", green" and blue" phosphor stripes or dots successively arranged on a face plate of the tube. Voltages V and V applied to the electrode plates P, and P, and to the plates P, and P, of beam convergence device F are selected so that the three beams BR, 86 and BB are made to cross each other at the position of the grill or mask Gp and thus made to land only on the corresponding phosphor stripes or dots. In this case, of course, the beams BR, BG and BB, while converging at the grill or mask Gp, are focused on the screen S.

The usual horizontal and vertical deflection means, as indicated by the yoke D, are provided for horizontally and vertically scanning the three beams simultaneously with respect to the screen S as in the conventional picture tube.

Thus, by supplying red", green" and blue" color video signals between the cathodes KR, KG and KB and the grid Gl, respectively, the three beams BR, BG and BB are intensitymodulated, whereby a color picture is produced on the color screen.

Referring now to FIG. 2, which shows only the plates P, and P, of the existing convergence device F, it will be seen that the beam BB passing therethrough is deflected by the electrical field E created between the plates P, and P,, and having its lines of equipotential indicated by the letter V. The amount of deflection of the beam passing therethrough is determined by the potential difference AV and the distance d between the plates P, and P,,. If the distance d between the plates P, and P, is maintained constant, the amount of deflection of the beam due to the field is solely due to the potential difference between the plates. As was previously mentioned, if the anode potential is applied to one of the plates, for example, to P,, and a lower potential, such as 200 to 300 volts lower, is applied to the other plate P,, variations in the anode potential, such as due to variations in the brightness of the picture, will cause variations in the potential gradient of the field and hence, vary the deflections of beams BB and BR with resulting misconvergence of the beams.

lf, with the above described convergence device, the lower potential V is chosen to be ground potential or zero, whereby to avoid the circuitry necessary to produce the potential 200 to 300 v. less than the anode potential V the potential gradient is very steep, as illustrated by the line marked V,, on FIG. 5, and the resulting electric field is too strong to properly deflect the beams.

In accordance with this invention, undesirable misconvergence of the beams caused by variations in anode potential when this potential is applied to the inner plates P, and P, of an electrostatic beam convergence device is avoided by providing an auxiliary electrode between the plates P, and P, and the plates P, and P,, which auxiliary electrode is at substantially the same relatively high potential as the inner plates P, and P,', For example, as is shown on FIG. 3, in which the illustrated tube is otherwise the same as that described with reference to FIG. 1, the electrostatic beam convergence device F according to this invention comprises, for the beams BB and BR emerging from focusing lens L along divergent paths in addition to the inner and outer plates P, and P,, and P and P,, respectively, disposed along the respective divergent paths at the inner and outer sides thereof considered with respect to the tube axis xx, auxiliary electrode means 12 and 12' disposed along the outer sides of the respective divergent paths and being spaced inwardly from the outer plates P, and P,'. Such auxiliary electrode means 12 and B2 are shown to have open areas, for example, as constituted by the spaces between parallel, conductive wires.

More particularly, referring to FIG. 4 which shows only the plates P, and P and auxiliary electrode means 12 therebetween, and bearing in mind that plates P, and P and auxiliary electrode means. 12 operate in the same fashion, it will be seen that the voltage'V applied to inner plate P end the voltage V, applied to the auxiliary electrode are substantially the same relatively high potential V,,, which may be the anode potential of the tube, while the outer plate P, is at a relatively low .potential V,, which may be ground potential. The voltages V,, V and V as thus applied, establish an electric field between the inner and outer plates P and P, which, in the region d thereof located between the inner plate P and the auxiliary electrode 12 and being traversed by the respective beam BB, has a relatively gradual potential gradient thatis,

maintained substantially constant irrespective of variations in the anode or other relatively high potential V, to avoid misconvergence of the beams due'to such variations.

In the embodiment of the invention, illustrated in FIGS. 3 and 4, the auxiliary electrode 12 is formed as a parallel array of straight conductors W,, WQ, W W,, W five conductors being shown for purposes of illustration, spaced from each other and extending transversely with respect to the longitudinal axis x-xof the tube. The auxiliary electrode 12 may be arranged substantially parallel to the plates,as shown, however, this is not necessary to realize the advantages of the invention. For simplicity of circuitry the potential V, applied to the outer plate P, may be chosento be ground potential, and

the potential applied to the auxiliary electrode 12 and the inner plate P may be chosen to be the anode potential of the tube, as mentioned above.

In this instance, the electric field and potential distribution between the plates P, and P and the auxiliary electrode 12 are as represented on FIG. 5. The electric field intensity and the potential distribution in a planeA A bisecting the space between the wires W and W on FIG. 4 are indicated at E, and V respectively, on FIG. 5, and the electric field intensity and potential distribution in a plane B- -B- passing through the center of the wire W are indicated by E and V,,, respectively. On FIG. 5, increasing potential and increasing intensity of the static field are indicated by the arrows V and E, and the arrow X indicates the distance from the outer plate P,, d, and d, indicate the distances from. the auxiliary electrode 12' to the outer plate P, and to the inner plate P respectively, while indicates the distance between the inner plate I and an imaginary plane P, located between the auxiliary electrode 12 and the inner plate P,, and at which the influence of auxiliary electrode 12 causes a potential V, to exist that is substantially greater than that obtained at such plane P, in the absence of electrode 12. 7

As was previously mentioned, if the auxiliary electrode 12 was omitted from the convergence device shown in FIGS. 3 and 4 and the illustrated potentials V, and V were applied to the plates P, and P a very steep potential gradient V,, would result, as shown on FIG. 5, and that steep potential gradient would not result in proper convergence of the beams. However, with the auxiliary electrode 12 provided according to the present invention between plates P, and P 2, a substantially linear potential gradient V A (Y,,) which is substantially more gentle than the potential gradient V, is present between the inner plate P and the plane P,. This potential gradient is maintained substantially constant in this region d,, between the inner plate P and the auxiliary electrode 12 which is traversed by the beam B irrespective of variations in the potential, for example, the anode potential, applied to the inner plate P The potential V, at the point in the field indicated by the plane P, is less than the potential V applied to the inner plate P As a result, an electric field of intensity Eb which is suitable for proper deflection of the beam B passing therethrough is obtained between the auxiliary electrode 12 and the inner plate P,, This electric field is due to the field created between the outer plate P,, which is at ground potential, and the inner plate P,, which is at the anode potential, permeating through the open areas of the auxiliary electrode 12 which is also at anode potential and reduces the potential gradient of the field in the region between the auxiliary electrode 12 the inner plate P Since the potential of auxiliary electrode 12 varies in accordance with any change in the anode potential applied to inner plate P the effect of electrode 12 is to maintain the potential gradient substantially constant in region :1, irrespective of variations in the relatively high anode potential of the inner plate P Further, on'FIG. 5, Ea indicates the field intensity in the region d, between electrode 12 and outer plate P,.

In a particular example of the embodiment of FIG, 3, the voltageapplied to the outer plate P, is 0 volts, the voltage (V V applied to both the auxiliary l2 and the inner plate P is kv., the distance d, betweenthe auxiliary electrode 12 and the outer plate I, is 5 mm. the distance d, between electrode 12 and inner plate P 9 mm., and the wires constituting the auxiliary electrode P have a, diameter of 0.2 mm., and a spacing between the wires of I mm with the foregoing dimensions and voltages, the fieldintensity Ea between electrode I2 and plateP, is 4,000 v./mm., while the field intensity Eb between the auxiliary electrode 12 and the inner plate P, is 1 l6 v.-/mm.,

so that there is asubstantial reduction-in the potential gradient associated with the deflection field traversed by the beam.

In the illustrated embodiment of FIG. 3, the electric deflection field to cause convergence is produced between the plates merely due to the potential difference between the anode potential and the ground potential, and there is no need toadditionally provide a potential lower than the anode potential by, for example, 200 to 300 volts. Although this field depends solely on the anode potential which may vary with respect to the ground potential, the potential gradient of the field in the region between the auxiliary electrode l2and the inner plate P is maintained substantially constant. Consequently, a desirable electric deflection field for proper beam convergence is obtained, and misconvergence of the beams due to variations in the anode potential is avoided. Furthermore, since only the ground and anode potential may be applied to the plates and auxiliary electrode, a simple convergence device requiring no additional circuitry nor terminals to apply additional potentials to thetube is obtained, and such potentials may be easily applied within the tube structure. However, potentials other than ground and the anode potential may be applied to the plate P,, and to the plate P and electrode 12, respectively, if desired, without departing from the principles of this invention.

By employing the auxiliary electrode disposed between the convergence plates and the potential relationship described above, static convergence of the beams may be easily maintained. Dynamic convergence of the beams may also be easily obtained by magnetic means (not shown) placed outside the tube. 1

It should be noted that the auxiliary electrode provided according to this invention may take many forms other than the parallel array of straight conductors spaced from each other and extending transversely of the tube axis, as in FIGS. 3 and 4, or extending parallel to the tube axis, as at 12A in FIG. 6A. Thus, for example, as shown in FIG. 6B, the auxiliary electrode 128 may be a plate formed of a conductive mesh of interconnected longitudinally and transversely extending conductive wires to define the necessary open areas.

In other embodiments shown in FIGS. 6C and 6D, the aux iliary electrode may be a plate 12C or 12D, respectively, having apertures therein to define the open areas, the apertures of FIG. 6D being more numerous and smaller in size than the transversely elongated apertures of FIG. 6C

It will be apparent that, in all of the above-described embodiments of the invention, the degree or extent of penetration of the electric field through the auxiliary electrode can be varied, so as to vary the potential gradient of the field in the region between the auxiliary electrode and the inner plate, and hence, the deflection of the traversing beam.

Although illustrative embodiments of electrostatic convergence devices according to this invention have been described in detail herein with reference to the accompanying drawings,

it is to be understood that the invention is not limited to those precise embodiments and that various changes and modifications may be made therein by one skilled in the art without departing from the scope or spirit of the invention.

We claim:

1. in a color cathode-ray tube in which beam-producing means direct a plurality of electron beams for impinging on respective color phosphors arranged in arrays on an electron receiving screen after passing through an apertured beamselecting means, focusing lens means are provided between said beam-producing means and said beam-selecting means for focusing the beams on said screen with at least certain of said beams emerging from said focusing lens means along paths that are divergent with respect to the tube axis, and beam convergence means are located between said focusing lens means and said beam-selecting means to deflect those beams which emerge along said divergent paths, whereby to cause convergence of said beams at an aperture of said beamselecting means; said convergence means comprising, for each of said beams emerging along a divergent path, inner and outer spaced plates disposed along the respective divergent path at the inner and outer sides, respectively, thereof considered with respect to said tube axis, auxiliary electrode means with open areas disposed along said outer side of the respective divergent path and being spaced inwardly from said outer plate, means for applying to said auxiliary electrode means and said inner plate substantially the same relatively high potential and means for applying to said outer plate a relatively low potential to establish an electric field between said inner and outer plates which, in the region thereof located between said inner plate and said auxiliary electrode means and being traversed by the respective beam, has a potential gradient that is maintained substantially constant irrespective of variations in said relatively high potential to avoid misconvergence due to said variations.

2. A color cathode-ray tube according to claim 1, in which said beams are made to intersect each other at a location within the tube between said beam producing means and said beam-selecting means, and said focusing lens means establishes an electric field having a center substantially at said location where the beams intersect.

3. A cathode-ray tube according to claim 1, in which said relatively high potential is the anode voltage of the tube, and said relatively low potential is ground potential, and said auxiliary electrode means is operative to relatively reduce said potential gradient of the field in said region thereof traversed by the beam.

4. A cathode-ray tube according to claim 1, in which said auxiliary electrode means includes a plurality of conductors spaced from each other in a parallel array.

5. A cathode-ray tube according to claim 4, in which said conductors extend transversely with respect to the tube axis.

6. A cathode-ray tube according to claim 4, in which said conductors extend longitudinally with respect to the tube axis.

7. A cathode-ray tube according to claim 1, in which said auxiliary electrode means is in the form of a plate having apertures therein to define said open areas.

8. A cathode-ray tube according to claim 1, in which said plate is constituted by interconnected longitudinally and transversely extending conductive wires. 

1. In a color cathode-ray tube in which beam-producing means direct a plurality of electron beams for impinging on respective color phosphors arranged in arrays on an electron receiving screen after passing through an apertured beam-selecting means, focusing lens means are provided between said beam-producing means and said beam-selecting means for focusing the beams on said screen with at least certain of said beams emerging from said focusing lens means along paths that are divergent with respect to the tube axis, and beam convergence means are located between said focusing lens means and said beam-selecting means to deflect those beams which emerge along said divergent paths, whereby to cause convergence of said beams at an aperture of said beam-selecting means; said convergence means comprising, for each of said beams emerging along a divergent path, inner and outer spaced plates disposed along the respective divergent path at the inner and outer sides, respectively, thereof considered with respect to said tube axis, auxiliary electrode means with open areas disposed along said outer side of the respective divergent path and being spaced inwardly from said outer plate, means for applying to said auxiliary electrode means and said inner plate substantially the same relatively high potential and means for applying to said outer plate a relatively low potential to establish an electric field between said inner and outer plates which, in the region thereof located between said inner plate and said auxiliary electrode means and being traversed by the respective beam, has a potential gradient that is maintained substantially constant irrespective of variations in said relatively high potential to avoid misconvergence due to said variations.
 2. A color cathode-ray tube according to claim 1, in which said beams are made to intersect each other at a location within the tube between Said beam producing means and said beam-selecting means, and said focusing lens means establishes an electric field having a center substantially at said location where the beams intersect.
 3. A cathode-ray tube according to claim 1, in which said relatively high potential is the anode voltage of the tube, and said relatively low potential is ground potential, and said auxiliary electrode means is operative to relatively reduce said potential gradient of the field in said region thereof traversed by the beam.
 4. A cathode-ray tube according to claim 1, in which said auxiliary electrode means includes a plurality of conductors spaced from each other in a parallel array.
 5. A cathode-ray tube according to claim 4, in which said conductors extend transversely with respect to the tube axis.
 6. A cathode-ray tube according to claim 4, in which said conductors extend longitudinally with respect to the tube axis.
 7. A cathode-ray tube according to claim 1, in which said auxiliary electrode means is in the form of a plate having apertures therein to define said open areas.
 8. A cathode-ray tube according to claim 1, in which said plate is constituted by interconnected longitudinally and transversely extending conductive wires. 